1. Field of the Invention
The present invention relates to a toothbrush which has an improved cleaning effect for details in the oral cavity such as interdental portions, cervical portions, pit & fissure where it is considered that plaques are liable to accumulate and it is difficult to remove the accumulated plaques with an ordinary toothbrush.
2. Description of the Related Art
Since plaques are apt to accumulate in interdental portions, cervical portions, pit & fissure and the like and yet it is difficult to remove the accumulated plaques, a toothbrush which can effectively clean these details in the oral cavity has been desired.
As the toothbrush for the purpose of cleaning these details in the oral cavity, there is known a toothbrush whose end is sharply tapered as disclosed in Japanese Unexamined Patent Publication No. 141923 of 1994.
Since this toothbrush has tapered filaments, it has an advantage that the end of the filament can be easily inserted into details in the oral cavity. On the other hand, since it has a relatively sharp end structure, it has a disadvantage that it injures or hurts the gum tissue. Further, since the stiffness of the filament is apt to be insufficient and the total area of the end surfaces of the filaments in contact with a site to be cleaned is small, it has such a disadvantage that its sweeping force is weak and a satisfactory plaque removal effect cannot always be obtained.
On the other hand, there is available a technique by which details can be cleaned with a composite monofilament whose end portion is divided into a plurality of superfine fibers. Examples of such a technique include Japanese Unexamined Patent Publication No. 277117 of 1994, No. 231813 of 1995 and No. 99604 of 1991. The term "composite monofilament" means that a single monofilament is formed by composing different materials of fibers.
Japanese Unexamined Patent Publication No. 277117 of 1994, for example, proposes a use of a composite filament prepared by coating a bundle of superfine fibers thereof with a synthetic resin, and removing the coated resin from a predetermined range of an end portion thereof to expose the superfine fibers.
Also, Japanese Unexamined Patent Publication No. 231813 of 1995 proposes a technique in which a composite monofilament is used which is prepared by spinning a polymer mixture containing a component easy to be dissolved, using a melt spinning machine, planting the obtained monofilaments in a handle, and immersing end portions of the monofilaments in a hydrolyzing agent such as an aqueous solution of sodium hydrate to have the end portions corroded so as to divide the end portions at random.
A brush using the above composite monofilaments whose each end portion is divided into several superfine fibers is soft and does not injure an object to be cleaned because the superfine fibers at the end of the monofilament are brought into contact with the object to be cleaned. In addition, the brush can exhibit appropriate stiffness because portions of the monofilament other than the end portion are integrated.
However, since the technique proposed by Japanese Unexamined Patent Publication No. 277117 of 1994 relates to a general brushes including car washing brushes, painting brushes, and the like, investigations on problems specific to toothbrushes are unsatisfactory and hence, a problem occurs when this technique is applied to a toothbrush.
In other words, Japanese Unexamined Patent Publication No. 277117 of 1994 discloses a technique in which a bundle of core filaments is integrated by coating with a resin. However, in such a composite monofilament, since water remains in a space between core filaments, various bacteria are apt to propagate in the space, which is insanitary. Further, the coated resin enclosing the core filaments has such a problem that it readily cracks and is inferior in durability.
Further, in the technique disclosed in Japanese Unexamined Patent Publication No. 231813 of 1995, since an end portion of the monofilament containing a component easy to be dissolved is divided into a plurality of fibers by the dissolution of the component easy to be dissolved, it is difficult to control the number and diameter of core filaments. In addition, like Japanese Unexamined Patent Publication No. 277117 of 1994, there is a fear that initial stiffness may not be maintained due to the cracking of the root of a separated portion during use.
A technique which overcomes the above problems to some extent is disclosed in Japanese Unexamined Patent Publication No. 99604 of 1991. A composite monofilament used herein is prepared by forming sheath/core type composite fiber portion (to be referred to as "composite portion" hereinafter) in which a sheath portion is studded with core portions made from a resin different from that of the sheath portion in a predetermined range of the monofilament from a planted base portion and a group of core filaments in an end portion from the composite portion by exposing only the core portions.
Since a resin is filled between the core filaments in this composite monofilament, water does not enter the planted base portion from the core filament base portion and there is no risk that the base portion of the core filament cracks during use. Further, since the number and the diameter of the core filaments can be controlled, a composite monofilament having a desired specification can be obtained and there is the possibility that it can be used as a composite monofilament for a toothbrush which lays stress on cleaning properties for details.
However, since the technique disclosed in this publication is directed to general brushes including car washing brushes, painting brushes, and the like, no consideration is given to specific conditions when this technique is applied to a toothbrush, and the configuration of a toothbrush making the most use of an advantage of this composite monofilament is not proposed therein.